A method for the inhibition of tumor metastases is described herein. The method makes use of the administration of certain castanospermine esters or their pharmaceutically acceptable salts.

The present invention involves a purified bioactive compound of the formula: ##STR1## wherein at least one of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are H or an acyl having less than about five carbon atoms. More specifically the preferred purified bioactive compound is (1R, 1R, 3R, 7S, 7aR)-3-hydroxymethyl-1,2,7-trihydroxypyrrolizidine.

The invention relates to novel mannosidase inhibitors, processes for their preparation and their use as therapeutic agents. The invention also relates to pharmaceutical compositions containing the compounds and their use as therapeutics

The invention relates to novel 3, 5, and/or 6 swainsonine analogues, processes for their preparation and their use as therapeutic agents. The invention also relates to pharmaceutical compositions containing the compounds and their use as therapeutics.

A method for synthesizing swainsonine salts and intermediates thereof comprising subjecting a compound of the formula I ##STR1## wherein R.sup.2 and R.sup.2' are the same or different and represent alkyl, halogen, alkenyl, alkoxy, cycloalkyl or aryl which may be substituted, to acid hydrolysis in the presence of a C.sub.1-4 alkanol to obtain a crystalline salt of swainsonine; and optionally, recrystallizing the swainsonine salt from a C.sub.1-4 alkanol. The reaction may be used in combination with one or more additional reaction steps.